Parathyroid Glands Physiology

Dr Taha Sadig Ahmed

• Four glands located on the posterior surface of the thyroid gland

• Secrete the polypeptide hormone PTH

• Decreased blood level of Ca++ stimulates the Parathyroids to secrete PTH

Regulation of PTH secretion

• Secretion of PTH is inversely related to plasma [Ca2+] because

• Plasma Ca2+ level is the dominant regulator of PTH secretion :

• Plasma Ca2+ level < 3.5 mg/dL stimulates PTH secretion

• Plasmna Ca2+ level > 5.5 mg/dL inhibits PTH secretion

Increase blood Ca++

Decrease blood Phosphate

Effects of PTHEffects of PTH

Effects of PTHEffects of PTH

Hypoparathyroidism• Causes • (1) Abnormal parathyroid gland Reduced

or absent synthesis of PTH• (2) Inadvertent قصد غير (by mistake) عن

removal of parathyroid gland during thyroid surgery

• This may lead to Tetany (increased excitability & hypersensitivity of nerves and muscles ) .

• Hypoparathyroidism is associated with hypocalcemia , but hypocalacemia can also accompany severe Vit D deficiency .

Signs & Symptoms of Hypoparathyroidism

• Positive Chvostek’s (facial muscle twitch) sign

• Positive Trousseau’s (carpal spasm) sign

• Delayed cardiac repolarization with prolongation of the QT interval

• Paresthesia• Tetany

Hhypoparathyroidism

• Tetany can be overt or latent• Manifested by 2 signs :• Chorostek’s sign: Tapping the facial nerve as

it emerge from the parotid gland in front of the ear causes contraction of facial muscles.• Trousseau’s sign :• Arresting (stopping ) blood flow to the forearm

for fe minutes ( e.g., by sphygmomanometer ) causes flexion at the wrist, thumb and metacarpophalangeal joints.

Carpal spasm ( overt tetany )Carpopedal spasm : sign of overt tetany

Trousseau’s sign

( test in latent tetany )

Hyperparathyroidism

• Adenoma ( tumor ) of parathyroid gland excessive PTH secretion

• Hypercalcemia results from combined effects of increased :

• (1) bone resorption, and • (2) intestinal and renal calcium absorption

Features of Hyperparathyroidism• Kidney : polyuria ,

polydipsia , renal stones • Bones : Rickets or

osteomalacia , osteitis fibrosa cystica ( soft bones with cyst formation: in picture arrows point to cysts )

• GIT : nausea , vomiting , indigestion , constipation , pepticulcer , pancreatitis

• Musculoskeletal : proximal muscle weakness

• CNS : depression , memory loss , psychosis , coma

Thanks